In injection molding a cap is often attached to a mold core with either a fixed vent or a moveable vent which facilitates ejection of a molded plastic article from a mold with pressurized gas. Air ejection is commonly used in the high volume molding of plastic containers, especially food packaging, such as margarine tubs, for example. Air ejection is advantageous because it reduces mold cost and allows ejection of deep-walled containers that are not extractable by conventional means.
Ordinarily, the cap is attached to the mold core with screws or a threaded rod. A core cap fixedly attached by screws to a molding core for molding a workpiece is disclosed in U.S. Pat. No. 4,660,801 wherein there is a fluid channel formed at the interface of a core base and core sleeve for ejecting gaseous fluid to the peripheral surface of the mold core. Other types of molding cores, as disclosed in U.S. Pat. Nos. 4,438,065 and 4,632,657, for example, have embodied additional pneumatic means to initiate ejection of the workpiece from the core. Screws and rods do not lend themselves to the molding of relatively small diameter containers, such as 35 mm film cans, for example, because there is not sufficient room for mold cooling channels. Also, screws can weaken the mold core substantially thus shortening mold life. Accordingly, it will be appreciated that it would be highly desirable to attach a cap to a mold core without screws or rods.
It is possible to connect workpieces without conventional screws by using a T-shaped fastening device. U.S. Pat. No. 3,109,214 discloses T-shaped fastener which is a bolt having a top portion adapted to receive another member having a socket. The two members are fixedly attached by inserting a T-shaped key member into the two members and rotating the member to be joined relative to the bolt. U.S. Pat. Nos. 4,129,395; 2,571,641; 2,140,132 and 847,253 disclose the use of T-shaped fastening devices. Accordingly, it will be appreciated that it would be highly desirable to attach a cap to a mold core with a T-connector rather than screws or rods so that small diameter articles can be molded efficiently.